Animal rights people often present their case (that human beings ought not to hold dominion over animals - viz, animals ought not to be eaten, hunted, kept as pets, kept on farms, used in research, bred for certain characteristics desired by humans, etc.) based on the grounds that it is immoral to deprive animals of their natural rights. In their view, the domestication of animals is an abomination, a perversion of what nature intended animals to be: free to live their lives as they see fit in an unsullied environment, without interference, exploitation or "oppression" by human beings.
The moral "case" that AR people make for abolishing animal domestication and the use of animals for human purposes hinges largely on how one views "natural," and their creation of a false dichotomy: either animals live oppressed and exploited under human dominion and therefore fail to fulfill nature's design (which is immoral), or they live free of human dominion, unoppressed and unexploited, and fit neatly into nature's scheme (which is moral).
Ignoring for the moment the silliness of the AR concept of natural morality, the dichotomy they create is ignorant of how evolution actually works.
Species - whether plant or animal - evolve adaptations. Adaptations are designed for one thing and one thing only: to maximize the chances that the gene pool of a species will survive. The contributions of those animals who are best adapted (at the moment) will be greatest, the contributions of those who are less well adapted at the moment will be less. Some crucial adaptations are used pretty much every day (like the digestive system), some may be used only once in a lifetime (the absence of scent in a newborn fawn). An adaptation can be an appearance (protective coloration) or a behavior (aggression and aggressive displays). Regardless of what the characteristics are, they must be judged according to whether or not the gene pool of a species survives. (What else would you use to judge a species' success, if not the perpetuation of its gene pool?)
From an evolutionary point of view, survival of a gene pool is all that counts - as long as that gene pool is perpetuated, the species is successful. As far as nature is concerned, how it is perpetuated is totally irrelevant.
And this crucial point is one that AR people either cannot or will not understand.
It is with this in mind that I highly recommend a book written by Stephen Budiansky entitled "The Covenant of the Wild: Why animals choose Domestication."
Budiansky makes the case that the capacity of animal species to accomodate themselves to human dominion is itself an adaptation. And he's right. Animal species that can be domesticated (deer, for example, cannot, at least the vast majority cannot) and that serve selfish human interests, whether economic (cattle, sheep, chickens horses and pigs, for example) or emotional/psychological (pets, especially dogs and cats) are assured of human protection, and their gene pools are perpetuated through human self-interest. So, by definition, the capacity of a species' gene pool to develop those physical, temperamental and behavioral qualities that humans value and preserve is itself an adaptation.
Thus the falsity of the dichotomy: it is entirely possible for animals to live under human dominion, and for this to be consistent with nature. Indeed, domestication itself is a perfectly reasonable and remarkably successful adaptive strategy.
I'll leave it to the reader to decide what level of morality or immorality should attach to the institution of animal domestication. Suffice it to say that nature really isn't much interested in AR ideology, notwithstanding AR self-serving definitions of what is and is not "natural."